PROJECT SUMMARY/ABSTRACT: Despite significant advances in breast cancer biology, limited progress has been made in developing targeted therapies for triple negative breast cancer (TNBC). TNBC is characterized by the absence of estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2 expression. TNBC accounts for 10?20% of all breast cancers yet it accounts for 40% of U.S. breast cancer deaths. There are no effective targeted therapies for TNBC and patients are managed with standard chemotherapy. Responses are usually brief and associated with progressive resistance and short survival. TNBC tumors contain a population of breast cancer stem cells (BCSC) that act as a major contributor to treatment resistance and treatment failure. BCSCs reside within a pro-inflammatory microenvironment that fuels their survival and self-renewal via the JAK/STAT signaling pathway. Current chemotherapies fail to take this into account and treat the entire body, resulting in systemic toxicities. Nanoparticles provide an avenue to achieve selective and efficient therapeutic delivery to diseased sites, thus avoiding off-target effects on healthy tissue. However, current nanoparticles exhibit inefficient delivery upon systemic delivery due to inadequate negotiation of biological barriers (e.g., immune cell recognition & sequestration, intracellular, vascular). We recently developed nanoparticles that integrate leukocyte membrane proteins into synthetic nanoparticles, (i.e., leukosomes) transferring immune cells' abilities to overcome these barriers and provide effective therapy for local inflammation. As we are aware of the regulatory hurdles for such a complex nanoparticle, we propose to improve the translational potential by simplifying their composition to incorporate specific leukocyte biomarkers crucial for negotiating these biological barriers. Within this strategy, we rely on our experience with identified leukocyte surface biomarkers necessary to avoid phagocytic sequestration (CD45, CD47) and active targeting (PSGL-1, LFA-1) of inflamed vasculature to develop simplified biomimetic nanovesicles (BNV). We will explore the potential of administering JAK and/or STAT inhibitors within leukocyte-based biomimetic nanoparticles (leukosomes & BNVs) to treat TNBC tumors pretreated with free taxane-based therapy to improve treatment efficacy while overcoming chemoresistance. We believe that leukocyte-based biomimetic nanoparticles will (a) retain the biological properties of leukocytes and (b) improve the pharmacokinetics and accumulation of JAK/ STAT inhibitors in a model of metastatic TNBC, compared to conventional liposomal-based platforms. Aim 1 will study the optimization of BNV selecting the minimal specific receptors able to endow our nanoparticles with leukocyte properties. Aim 2 will evaluate the targeting and pharmacokinetics of leukosomes in vivo using metastatic human TNBC patient derived xenografts (PDX). Aim 3 will study the efficacy and safety of leukosomes in vivo in the TNBC PDX model. The best formulation of BNVs from Aim 1 will be tested separately from leukosomes for biodistribution and pharmacokinetics (Aim 2) and antitumor efficacy (Aim 3).